This invention relates generally to packaging or wrapping machinery and more specifically to a servo control system incorporated in the packaging machinery for maintaining synchronism between the product flow, wrapper film flow and the cut-off and end-sealing assembly such that precise uniformity in the wrapped articles is achieved.
In horizontal wrapping machinery, flexible film, such as cellophane, polyethylene, paper or foil, is drawn from a supply roll and passed through a film former as the articles to be wrapped are fed along a conveyer at spaced intervals. The film former creates a tube-like enclosure about the articles and the two longitudinal edges of the film comprising the tube are pinched between one or more pairs of closely spaced finwheels whereby the longitudinal fin seal is formed on the bottom of the packages. Next, the film tube containing the articles being wrapped is passed between transversely disposed rotating or oscillating end-sealing and cut-off members which severs the tube between the articles while creating a transverse end seal on the individual packages. In such machines, the finwheels are the means for drawing the film from the supply roll and it is imperative that they by synchronized with the product conveyer and with the end-seal and cut-off knives if jamming of the machine or the stretching of the film is to be avoided. Also, where the film is preprinted with graphic information such as advertising, the article must be properly centered in the package as it is being formed and the cut-off knives must sever the wrapper at predetermined spaced locations relative to an index mark on the film if uniformity of appearance in the separate packaged articles is to be maintained.
In the past, synchronism between the conveyer, the finwheels and the end-seal/cut-off knife assembly has been maintained through the use of rather complex arrangements of gears, belts and pulleys. Typically, a so-called Cleveland Variator device, which has a high precision variable speed friction drive is made to operate in conjunction with an electric-eye correction module to sense out-of-sync conditions and to allow adjustment of the relative speed of the units to be synchronized. Each time the packaging machine was to be used to wrap different sized articles, it became necessary to readjust components of the mechanical drive system, typically by turning micrometer-like calibrated knob associated with the aforementioned variable speed friction drive. The mechanical approach to synchronization tended to be costly and added to the complexity of the machine, making setup, operation and maintenance somewhat difficult and adding to the amount of nonproductive down-time of the machine.
In addition, in the mechanical sychronization approach of the prior art, it has not generally been possible to advance or jog the finwheels independently of the conveyer and end-seal/cut-off blades. That is to say, in prior art designs, during initial threading of the film into the machine, it is necessary to run the entire machine at its preset production rate. This makes it relatively more difficult to set up the wrapping machine when it becomes necessary to change the type of film being used.